SAN JOSE — At least 21 people were treated for burn injuries after participating in a firewalk Thursday night at a Tony Robbins event downtown, including at least three individuals who were taken to the hospital, according to a San Jose fire captain.

The people who suffered various second- and third-degree burn injuries were among more than 6,000 who attended the event led by the self-help author, Unleash the Power Within, at the San Jose Convention Center.

After the event, which ended about 11 p.m., the crowd walked across the street to a park where 12 lanes of hot coals measuring 10 feet long and 2½ feet wide rested on the grass.

Jonathan Correll, 25, decided to check out what was going on when “I heard wails of pain, screams of agony.” He said one young woman appeared to be in so much pain “it was horrific.”

Correll, a San Jose City College student, said he saw between 10 to 15 people being treated.

It took about 90 minutes for people to walk across the coals. It is not known how many of the people who attended the conference took part in the firewalk.

San Jose fire Capt. Reggie Williams said event organizers had emergency personnel on standby, and they treated 21 people at the scene. Firefighters responded to 911 calls for three of the people who suffered more serious burns, Williams said.

Later in the night, firefighters responded to more 911 calls from people in area hotels who had suffered burn injuries. Williams did not know how many of those people had already been treated.

A statement released Friday from Robbins Research International Inc. said, “We have been safely providing this experience for more than three decades. … We continue to work with local fire and emergency personnel to ensure this event is always done in the safest way possible.”

On Robbins” website he promotes “The Firewalk Experience,” a process where people walk across coals between 1,200 and 2,000 degrees Fahrenheit.